Thermostatic element



Re. 22,754 l May 14, 1946.

D. w. Al-:RNATHY THERMosTA'rIc Fmsmmw Original Filed 'June 9, 1942 ...1.1M @wifi `avid WAZ -Reisen-ed May'14, 1946 l Davia w. Abernathy,

poration of Illinois Original No. 446,332, June issue May 2, 1945,

11 Claims.

This invention relates generally to therm ostatic electrical switches and more particularly to a novel and improved switch of this'kind especially adapted to be used in connection with the heater employed in heating Iwound tresses of hair as for the permanent Waving thereof.

`The primary object, of the invention is to provide a novel and improved thermostatic electrical switch structure.

A further object of the invention is to provide a. novel bimetal type of thermostatic swltch which is simple and compact and member is not subject to undue stress at low temperatures.

Another object is to provide an improved thermostatic switch having a novel mounting for the heat responsive and movable contact structure thereof. v

A further object of the invention is to provide a novel and improved thermostatic switch which will respond accurately to h'igh temperatures for which it has been adjusted.

A further object of the invention is to provide "Chicago, Ill., assignor to Products Development, Inc.,

Chicago, Ill., a cor- No. 2,349,126, dated May 16, 1944, Serial 9, '1942. Serial N0. 591,452

Application for re- (Cl. EGO-138) in which the bimetal v in the waving process.

a novel thermostatic switch unit which may be easily associated with the shell of a heater clamp sothat the switch is immediately responsive to the heat.

Other objects and inventions lie in the specific l constructional details of the thermostatic switch.

With the foregoing and other objects in view which will appear as the description proceeds, the invention consists of certain novel features of construction, arrangement and combination of parts hereinafter fully described, illustrated in the accompanying drawing, and particularly pointed out in the appended claims, it being understood that various changes in the form, proportion, size and may be made without departing from the spirit or sacrificing any of the advantages of the invention.

minor details of the structure For the purpose of facilitating an understanding of my invention, I have illustrated in the accompanying drawing a preferred embodiment thereof, from an inspection of which, whenconsidered in connection with the following descrip- A tion, my invention, its mode of construction, assembly and operation, and many of its advantages should be readily understood and appreciated.

kReferring to the drawing in which the same characters of reference are employed to indicate corresponding or similar partsy .throughout the several figures of the drawing:

Fig. l is a perspective view of a. heater clamp such as used in heating wound tresses of hair in r mostats or readjust them often,

the permanent waving thereof, having my invention incorporated therein.

Fig. 2 is a perspective view of one of the jaws of the clamp broken away in order to show th'e inner construction thereof.

Fig. 3 is a sectional view taken the clamp jaws substantially along the line of Fig. l.

Fig. 4 is a side .static switch.

Fig. 5 is a perspective view of the switch unit prior to being installed in the shell of the clamp jaw, and having certain parts broken away and in section for clarity of illustration.

In the permanent waving of hair by means of electrical heaters, it trol the energizing electricalci-rcuit thermostatically for the purpose of maintaining the temperature of the heaters substantially constant. This is desirable for reasons of control and unifromity In the manufacture of elevational view of my thermothe heating clamps associated with each respective clamp and'is adjusted to open the circuit to the heating elements when a certain predetermined temperature is attained at the clamp jaws. The types of thermostatic controls heretofore used have been constructed in such fashion that the bimetallic elements thereof, sometimes referred to as the bimetals, have been subject to undue .stress during the early life of the units and as a result their characteristics have tended to undergo distortional ch'anges from' those contemplated. Hence it hasbeen necessary to replace the theror in some other manner compensate for the change in characterw istics. Either excess heat or fluttering may result from misadjusted thermostatic elements.

Probablyr the greatest cause for distortional strain occuring is that reverse stress is placed upon the bimetal when it is subject to low temperatures, as for example, when transported in cold weather or stored in an unheated warehouse. Even if the thermostatic element is merely subdifier'ent from those and maintained that way for a long while, its characteristics may change perceptibly due to the stress and strains which inevitably develop under such conditions.

4My new invention besides eliminating the disadvantages above described, provides a thermostatic switch which is so small and compact that j instead of being associated with the heater clamps through one of has been customary to conthe thermostatic element is appears from the may more accurately respond to the proper temperature and not depend for operational heat upon that portion of the heat from the element whichv is conducted to it along the shell as has been the case with prior elements.

Referring now to the specic details of a device embodying the invention, the reference character I Il designates generally a clamp of the type used in giving the so-called machine pennanent wave. The clampY I3 comprises a pair of clamp arms Il terminating in elongated transverse jaws I2 which have the inner surfaces I3 thereof concave and opposed in order to hold and heat therebetween a tress of hair which has been suitably wound or formed to some desired configuration. Electrical wires I4 supply current to a heating element which has been generally shown as a. mica member I 5 (Figs. 2 and 3) wound with resistance wire I6, embedded in a ceramic material or the like Il and the whole being retained by a covering member I3. The outer portion of each of the Jaws I2 comprises a metal shell I9 which may have its edges engaged over the covering member I3 as shown at .20..

vat a point immediately adjacent to the heating velement and hence That portion of the clamp III above-described l is generally well known and per se is not part of my invention.k However, it is of importance here as it demonstrates an important environment in which my invention is particularly useful.

'I'he shell I9 is preferably fashioned from sheet metal and may be integrally formed with the arms II. Such arms II are provided with ears 2| which cooperate with a pin 22 extending therethrough so that the arms II may pivot with respect to one another. A wire spring 22* norl mally urges the clamp jaws I2 into engagement with one another. y

Integrally formed with the shell I9, I have provided a cavity 23 which is on the outer side of one o1' the jaws I2. The shell being formed of sheet metal, the cavity 23 is struck therein at the time of the drawing or forming of said shell. Within this cavity 23, I have aillxed my thermostatic switch element 2l. Of course, the cavity outside o! the clamp member 2 as a somewhat rectilinear protuberance 25 upon the outer surface of the shell I 9. The thermostat is thus seen to be almost immediately next to the heating element contained in the covering member I3. Hence heat from the element will impinge directly upon the thermostat switch 24 and cause same to operate in the desired manner.

The thermostatic switch 2l comprises an elongated substantially rectilinear base member 26 adapted to fit snugly into the cavity 23. T'he base member has upwardly extending Ilanges 21 along portions of its longer edges which are adapted to engage the inner walls of the cavity 23. 'I'he'base member 28 is lined with a layer of ber insulating paper 23. At one end, the base member 23 has a pair of integrally formed lugs 29 which engage the ends III of a small strip 3| f resilient metal such as phosphor bronze, which stripis laid across the end of the base member 23. 'Ihe central portion of the strip 3| is bent upwardly as shown at 32 and an upwardly pro- Jecting electrical contact point 33 is provided thereon. Obviously, the mounting of the contact point 33 is more or less resilient although for all practical purposes this contact point is considered as a xedcontact. It will be noted that for heat insulation I have provided a layer of as- 4I toward and into with the xed contact 33. Asl the mount leg 38 v bestos paper 34 between the ber paper layer 2l and the ends 30 of the strip 3|.

The opposite end of the `base member 26'is provided with a second strip 35 of resilient metal such as phosphor bronze engaged beneath bent over lugs 36 and insulated by said layer oi" fiber paper 23 and the asbestos paper 34. This strip 35 is at and is provided with an arm portion 31 extending longitudinally along the base 26 toward but substantially short of the contact support 3| and then is bent back upon itself in substantially U-shaped form as at 38 to provide a nat leaf .spring arm which terminates at 39 overlying the portion of the strip anchored by the lugs 33.

At the termination point 33, I have welded bimetal member 40 and a. coextensive but somewhat longer strip of resilient metal 4I which projects freely ybeyond the spring mount 35 and is provided on the free end thereof with a downwardlyy Aextending contact point 42 normally adapted to engage with the contact point 33, As will be noted, the bimetal member 40 and the movable contact carrier 4I project cantilever fashion longitudinally over and beyond the spring leg 38 toward the fixed contact support 3|. 'I'he contiguous ends of all three .members 39, 40 and 4I are so intimately 'joined together by the welding that they form a solid block 39' which moves as a unit when the supporting spring arm portion 38 of the mounting strip is flexed. The block 39' is tapped for the'reception of an adjusting screw I3, the tip of which is adapted to project below the block and contact the underlying surface of the strip 35 freely and slidably.

Good results in adjustment have been secured by having the arms 3l and 38 of the contactsupporting member 35 so biased that they tend to close upon one another with the integral joint between the arms serving more or less as a pivot enabling the arms to be swung open and closed. Thus, screwing the adjusting screw -down causes the arms to separate as seen in Figs. 4 and 5 and tips the free or contact-carrying end of the strip variable-pressure engagement the underlying leg 31 beyond a certain point, the tension of the carrier-strip 4l is increased due tothe engagement of its contact end with the xed contact 33, and the active or free end ofthe bimetal strip 40 is depressed to is flexed away from carryit proportionately away from the carrier strip to increase the space through which it must travel before acting on the carrier strip. In this way the temperature at which the switch will act can be selectively increased.. By unscrewingthe adjusting screw 43, the arms 31 and 33 are allowed to approach one another and thus relieve the pressure with which the contact-carrying strip 4I approaches the fixed contact 33 and decrease the spacing between rier strips. thus reducing the temperature at which the switch will act. In this manner, thev switch can Ybe adjusted fairly accurately for operation at any predetermined temperature within a substantial range. More importantly, substantial manufacturing variations in the various parts of the assembly can be tolerated conveniently because adjustment of the switch to operate at any predetermined temperature within said range can be eifected with ease and accuracy.

It will` be noted that at its Welded terminus the bimetal member lll is 'somewhat thicker than the remainder of its body, or, obviously. a spacer may the bimetal and carbe interposed to afford such thickness, and hence face of the bimetal member 40 and the carrier strip 4I affording ample clearance to permit some heat-induced flexure of the bimetal member such as may without the bimetal engaging against the adjacent face of the carrier strip 4I. Because of this freedom of self-adjustment in response to non-operating heat, there is obviously no stress generated in the bimetal which would cause it to become permanently strained.

As for .the reaction of thebirnetal 4U, when it is subject to low temperatures, that is alsov permitted in order that there be no reverse stress placed thereupon. It will be noted that the bimetal Ill is substantially Iloating, that is to say, if it should tend to curl downwardly thereis nothing to `impede its movement. Considerable space may be provided tc accommodate it in even subzero temperatures. The bimetal thus retains its resilience throughout various temperature changes so that in use it will respond to the exact temperature for which it has been adjusted. At that temperature the bimetal 40 moves upwardly, as viewed in Fig. 4, engages against the bottom face of the contact-carrying strip r4I and exes the latter up to lift the contact 42 from the contact 33. Inasmuch as there has been no distorting strain placed upon the bimetal, its resilience remains unirnpaired so that while it releases upon cooling to enable reversing movement of the strip 4l, return of the latter to contact-closing position will be gradual, eliminating utter.

In prior thermostatic switches, thebirnetal has usually been in some manner connected with the movable contact-carrying member or has itself been such member so that where thel bimetal is subjected to lo'w temperatures it is considerably stressed since its motion is opposed by the fixed contact. This may result in a permanentstrain or distortion as suggested above. As vto the reverse reaction' of the element in warm weather, where the bimetal is associated with the contact directly, a certain amount of the tension between the contacts is relieved, making for uncertain break temperatures.

The supporting strips 3| and 35 are provided with wire leads I5 and 4B, respectively, whereby the switch 24 may be connected into the circuit be caused by ordinary warm weather,

' one end of said bimetal strip being connected to the second end of said spring, whereby said of the electrical 'heater element in a well known manner. l In view of the above description it should be apparent that I have provided a novel and ingenious thermostatic switch which is not onlyefcient and positive in operation, but which is compact and well arranged so that it may be incorporated into a small space such as the cavity 23 of the clamp as described herein. l

It is believed that my invention, its mode of construction and assembly, and many of its advantages should be readily understood from the foregoing without further description', and. it should also be manifest that while a preferred embodiment of the invention has been shown and described for illustrative purposes, the structural details are nevertheless capable of wide variation within the purview of my invention as detlned in the appended claims. i

What I claim and desire to secure by Letters Patent of the United States is:

1. A thermostatic switch adapted to open an electrical circuit at a predetermined temperature,

comprising a basel member, a resilient ilxed contact-supporting member attached to said-base'at one end thereof and having a contact provided thereon, resilient movable contact supporting means attached to the base member at the opposite end thereof and comprising a strip bent upon itself to form a substantially U-shaped spring, one Aend thereof being xed to-the base member, a bimetal strip and a resilient contactcarrying strip having a contact on the free end thereofvfor engagement with said xed conta'ct, the other end of said contact-carrying strip and springmay control the pressure between the contacts.

2. A thermostatic switch as dene'd in claim l wherein the free end of said bimetal strip is adapted to engage with a side of said resilient strip for causing disengagement between said contacts when the bimetal member is 's'ubjectto said predetermined temperature.

3. A thermostatic switch as deiined in claim l wherein the free end of said bimetal strip is adapted to engage with a side of said resilient strip for causing disengagement between'said contacts when the' bimetal member is subject to said predetermined temperature, but is normally spaced from .said resilient strip and `free to bend away from said strip whenthe temperature is low.

4. A thermostatic switch adapted to open an electrical circuit at a predetermined temperature, comprising a base member, a fixed contact, mounted at one end of said base, resilientl movable contact supporting means attached to the base member at'the opposite end thereof and comprising a strip bent upon substantially U-shaped spring, one end thereof being fixed to the base member, a bimetal strip and -a resilient contact-carrying strip having a contact on the free end thereof for engagement with said ilxed contact,vone end of said bimetal strip and the other end of said contact-carrying strip being connected to the second end of said spring, whereby said spring maycontrol the pressure between the contacts.

5. In combination in a thermostatic electrical switch of the characterdescribed, a pairi of contacts, one of said contacts being movable relative to the other and having an elongated ilexible carrier strip, a bimetal strip, a mount having a movable portion thereof in support of both said carrier strip and said bimetal strip in substantially coextensive superimposed relation with the bimetal strip in juxtaposition to said mount portion andthe contact end portion of the carrier strip projecting beyond the adjacent end of the bimetal strip, and means for adjusting the position of said movable mount portion to alter the tension of said carrier strip with respect to said contacts and to vary the spacing of the active end of the bimetal strip from the carrier strip so as to predetermine the force with which the bimetal strip must act and the distance its active end must travel to ilex the-carrier strip and separate the contacts, and thus the temperature at which the switch will act.

6. In'combination in a thermostatic electrical switch of the character described, a relatively xed contact, a flexible strip having a contact separably engageable with the fixed contact to close an. electrical circuit therethrough, a bimetal strip, and a movable mount supporting itselfy to forma bimetal strip must act upon the contact-carrying strip to flex it into movement relative to the fixed contact and thereby the temperature at which the switch becomes active.

7. In combination in an electricalswitch f the vcharacter described, a relatively fixed contact, an elongated resilient carrying strip having a 'y contact thereon movably engageable with said xed contact and adapted to act under tension in maintaining the contacts pressed together, a substantially U-shaped spring mount having said carrying strip secured to one arm thereof and having the other arm mounted in iixed position, the arms of said spring mount being biased normally to collapse together and relieve the contactpressing tension of said carrying strip, an adjusting screw threaded through the strip-carrying leg of said mount and engaging at its tip against the opposing face of the opposite leg adapted when screwed down to separate said legs and selectively adjust the contact-pressing ten-v sion and ilexure of said contact-carrying strip. and a. bimetai strip carried by saidspring mount to act upon the carrying strip to move it relative to the ilxed contact.

8. In combination in a thermostatic switch unit, an elongated base of small size having sides adapted to fit snugly against the inner sides of a housing therefor, a fixed contact mounted adjacent one end of the base inside of the planes of said sides, a movable contact cooperating electrically with said fixed contact and having a carrier strip extending therefrom within the planes of said sides to adjacent the opposite end of the base, a mount for said strip at said opposite end of the base supporting the strip cantilever fashion, and a-bimetal strip also supported cantilever fashion by the strip mount and in coextensive spaced relation to the carrier strip butextending short of said fixed contact to ex freely under l the influence of temperature changes, said bimetal strip being engageable with said carrier strip in' response to certain temperature conditions to move the contact endthereof relative to the fixed contact.

9. A switch unit as defined in claim 8 in which the sides of the base are extended as flanges projecting protectively beyond the plane ofthe contact-carrying strip whereby the unit can be handled safely.

ionwithout stress upon the bimetal'strip where- 'by to predetermine the force with which the 10. In combination, in an electrical switch of the character described, a relatively xed contact, an elongated resilient carrying strip having contact thereon movably engageable with said flxedcontact and adapted. to actunder tension in maintaining the contacts pressed together, a substantially U-shaped spring mount having said carrying strip secured to one arm thereof and having the other arm mounted in fixed position, the arms of said spring mount being biased normally to collapse together and relieve the contact-pressing tension of said carrying strip, an

adjusting screw threaded through the strip-carrying leg of said mount and engaging at its tip against the opposing face of the opposite leg adapted when screwed down to separate said legs and selectively adjust the contact-pressing tension and flexure of said contact-carrying strip, and a bimetal element mounted on the strip-supporting leg of the mount in an adjustably spaced relationship to the strip'and adapted to respond to predetermined temperature in any adjusted relationship to flex the contact-carrying strip for opening the contacts.

11. In combination in a switch unit, an elongated base, a nxed Contact mount insulatemy secured adjacent to one end of `said base, a movable contact mount insulatedly secured adjacent to the opposite end of said base and including a movable arm. a flexible `contact strip mounted on said movable arm and extending into overlapping relation to said fixed contact mount, said fixed contact mount and said strip having respective relatively separable contact points thereon, said movable arm being formed with a resilient support portion normally exerting tension on said strip in a direction away from said iixed contact whereby said strip is held in relatively untensioned relation to said iixed contact, and means associated with said arm and movable in a direction tending to oppose the tension on the strip whereby said arm is moved into relatively adjusted strip-tensioning position to eii'ect selectively variable pressing together of the contacts, and a, bimetal element mounted in assembly with and between the contact-carrying strip and the movable mounting arm, with the bimetal element in free-floating relation to the strip and movable with said arm.

DAVID W. ABERNATHY. 

